DSPSR: Digital Pulsar Signal Processing / Bugs / #57 Different values of -S to dspsr wipe giant pulses from output

Haydon Knight - 2014-12-08

Investigating at other skip factors yields:

skip GP_archive max_flux offset
0 skip0/pulse_42856335260.ar 0.177853 84.1888
20 skip20/pulse_42856335853.ar 0.19393 104.147
40 skip40/pulse_42856336447.ar 0.203661 124.106
60 skip60/pulse_42856337041.ar 0.180002 144.15
80 skip80/pulse_42856337635.ar 0.192757 164.109
100 skip100/pulse_42856338228.ar 0.184013 184.154

Here 'offset' is the number of seconds the MJD of the GP archive is past the start of the input data file.

Clearly (a) the same GP is being found over and over; (b) it is being placed in archives with the wrong MJD

At skip factors of 120s+ the GP is not found (For '-S 120' only 80s of data is processed so the GP is not found).

Clearly 'dspsr -S' does not work.

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Haydon Knight - 2014-12-09

The problem seems to be with the FITSFile loader - no capability to seek (i.e. change the current_byte counter) was built in. Adding in "seek_bytes" and "seek" functions appears to fix the problem.

Here is the code I used (I don't think the return value to seek_bytes is right but it seems to work):

//! Override File::seek_bytes
int64_t dsp::FITSFile::seek_bytes (uint64_t bytes)
{
// Do nothing as FITS does not need to adjust its file descriptor

// Not sure what to return so return 0
return 0;
}

//! Override Input::seek
void dsp::FITSFile::seek (int64_t offset, int whence)
{
const unsigned nchan = get_info()->get_nchan();
const unsigned npol = get_info()->get_npol();
const unsigned nbit = get_info()->get_nbit();

if( nchannpolnbit % 8 )
throw Error(InvalidState,"dsp::FITSFile::seek",
"nchannpolnbit (%d bits) is not a whole number of bytes, so cannot seek for this mode of data",
nchannpolnbit);

const unsigned bytes_per_sample = (nchannpolnbit) / 8;

// Adjust current_row and byte_offset depending on next sample to read.
uint64_t next_sample = current_byte / bytes_per_sample;

switch (whence) {

case SEEK_SET:
if (offset < 0)
throw Error (InvalidRange, "dsp::FITSFile::seek", "SEEK_SET -ve offset");
next_sample = offset;
break;

case SEEK_CUR:
if (offset < -(int64_t)next_sample)
throw Error (InvalidRange, "dsp::Input::seek", "SEEK_CUR -ve "
"not allowed");
next_sample += offset;
break;

case SEEK_END:
if (!get_info()->get_ndat())
throw Error (InvalidState, "dsp::FITSFile::seek", "SEEK_END unknown eod");

if (offset < -int64_t(get_info()->get_ndat())) throw Error (InvalidRange, "dsp::FITSFile::seek", "SEEK_END -ve offset"); next_sample = get_info()->get_ndat() + offset; break;

default:
throw Error (InvalidParam, "dsp::FITSFile::seek", "invalid whence");
}

current_byte += next_sample * bytes_per_sample;
}
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Haydon Knight - 2014-12-09

Now I seem to get dspsr repeating the message:

Tempo2::Predictor::phase epoch=56559.8 frequency=192.64

and running very slowly. Standard dspsr takes about 8.2s to fold 5s of data; new dspsr takes at least a very long time (> 6minutes) although it may be in an infinite loop.

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Different values of -S to dspsr wipe giant pulses from output

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#57 Different values of -S to dspsr wipe giant pulses from output

~/astro/dspsr/Signal/Pulsar/dspsr -b 256 -N J0534+2200 -s -K ~/data/fitsfiles/J0534+2200/20130925A/20130925A_0006.fits -S 100

The threshold for being a GP is approximately 0.04; this pulse goes from being a GP to being noise.

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